1. Preheat oven to 350°F and grease a 9×13 inch pan or 9-inch springform pan.
2. Peel, core, and chop apples, then toss them with cinnamon and a little sugar.
3. Prepare crumb topping by mixing flour, sugar, cinnamon, and cold butter until crumbly.
4. In a bowl, mix cake ingredients including flour, sugar, butter, eggs, sour cream or Greek yogurt, and a yellow cake mix if using.
5. Pour cake batter into the prepared pan and spread evenly.
6. Layer the cinnamon-coated apples evenly over the batter.
7. Sprinkle the crumb topping over the apples.
8. Bake for 45-55 minutes or until a toothpick inserted in the center comes out clean.
9. Allow cake to cool slightly before serving.
10. Optionally, mix powdered sugar and milk to create a glaze and drizzle over the cake.
11. Serve warm or at room temperature for breakfast, dessert, or a snack.
12. Store leftovers at room temperature for 2-3 days or freeze for up to 3 months.